In years past, Windows software upgrades have coincided with improvements in computer processing speed, memory and graphics.

This time, Microsoft is requiring Windows users to switch to a radical new interface. Instead of the traditional keyboard and mouse, Windows 8 users must master a touch screen that works in concert with keyboard and mouse commands.

"It doesn't surprise me that people wouldn't be in a rush to buy a new PC just because it has a new operating system," says Gartner analyst Steve Kleynhans, Gartner's mobile and client computing analyst. "If Microsoft somehow demonstrates through its marketing that users can do new things in new ways, that might start to get people interested."

On Oct. 25, the day before Windows 8 officially went on sale, Avast polled 1.6 million users of its PC anti-virus product, and got 350,000 responses, including 135,329 from U.S. Windows users.

Some 65% of U.S. users replied from PCs running Windows 7, while 22% still used Windows XP and 8%, Windows Vista.

Six of 10 respondents were aware of Windows 8, indicating Microsoft did a good job of marketing the product in the months leading up to the Windows 8 launch, says Jonathan Penn, Avast's director of strategy. But only 9% of U.S. respondents said they would accelerate a decision to buy a new computer just to have Windows 8, while more than 70% said they planned to stick with what they have.

Reports of software applications designed for earlier versions of Windows not working well on Windows 8 haven't helped, says George Otte, CEO of Geeks on Site, a repair service. "Windows 7 works just fine," Otte says. "It's not a major priority to make a change, especially if there might be apprehensions about bugs."

Microsoft's large corporate customers are expected to be even slower than consumers in embracing Windows 8. Many are still in the process of deploying Windows 7 PCs, the 2009 upgrade from Windows Vista.

"The simple adjustment of not having a 'start' button will be a hurdle," says Karl Volkman, chief technology officer at SRV Network, an Internet service provider.

Microsoft is not releasing sales figures for Windows 8. But a few days after the Windows 8 launch, CEO Steve Ballmer announced at a tech conference that the company sold 4 million Windows 8 upgrades and tens of millions of licenses to businesses. Ballmer noted that the "level of embrace from enthusiasts ... is very, very high."

Avast's poll of U.S. Windows users found 16% planned to purchase a new computer. While 68% indicated they would get one of the new Windows 8 models, 30% planned to buy an Apple iPad touch tablet, and 12%, an Apple Macintosh computer.

"Many households already have multiple PCs, and people are keeping their computers longer," observes Penn. "More people are going to the iPad as their second or third computing device."